Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$38.71	9.143%	$42.2493	$42.25	$42.25	$42.20
Purchase #2	$18.76	8.506%	$20.3557	$20.36	$20.35	$20.40
Purchase #3	$58.42	10.823%	$64.7428	$64.74	$64.75	$64.70
Purchase #4	$240.93	6.737%	$257.1615	$257.16	$257.15	$257.20
Purchase #5	$178.67	9.784%	$196.1511	$196.15	$196.15	$196.20
Purchase #6	$60.43	11.135%	$67.1589	$67.16	$67.15	$67.20
Purchase #7	$243.25	10.513%	$268.8229	$268.82	$268.80	$268.80
7 purchase totals =	$839.17		$916.6422	$916.64	$916.60	$916.70